MAGNETIC INDUCTIVE FLOW METER
Description:
Magnetic inductive flow meter
Technical field:
The invention relates to magnetic inductive flow meters according to the preamble of
claim 1.
Background Art:
Magnetic inductive flow meters use a measuring method that is based on Faraday's law
of electromagnetic induction. The first basis for the magnetic inductive measurement of
the flow velocity of fluids was reported in 1832 in a publication by Michael Faraday.
Modern electronic switching technology in conjunction with alternating magnetic fields
made it possible to overcome the separation of the useful signals, proportional to the
flow velocity, from interference signals, which occur in electrochemical processes during
the generation of the magnetic field at the electrodes used for signal decoupling. Thus,
nothing seemed to stand in the way of the wide industrial use of magnetic inductive flow
meters.
The measuring principle of magnetic inductive flow meters utilizes the separation of
moving charges in a magnetic field. The conductive fluid to be measured flows through
a tube which is made of nonmagnetic material and whose interior is electrically
insulated. A magnetic field is applied from the outside by means of coils. The charge
carriers present in the conductive fluid, such as ions and other charged particles, are
deflected by the magnetic field: the positive charge carriers to one side and the negative
charge carriers to another side. A voltage, which is detected with a measuring device,
arises owing to the charge separation at measuring electrodes arranged perpendicular
to the magnetic field. The value of the measured voltage is proportional to the flow

velocity of the charge carriers and thereby proportional to the flow velocity of the
measuring fluid. The flow volume can be determined over time by integration.
In magnetic fields generated by pure alternating voltage, induction of interference
voltages occurs in the electrodes, which must be suppressed by suitable but costly
filters. For this reason, the magnetic field is usually generated by a clocked direct
current of alternating polarity. This assures a stable zero point and makes the
measurement insensitive to effects by multiphase substances and inhomogeneities in
the fluid. In this way, a usable measuring signal can also be achieved at a low
conductivity.
If a measuring fluid moves through the measuring tube, according to the induction law a
voltage is present at both measuring electrodes, which are arranged in the measuring
tube perpendicular to the flow direction and perpendicular to the magnetic field. This
voltage in the case of a symmetric flow profile and a homogeneous magnetic field is
directly proportional to the average flow velocity. The inductive flow measuring method
is capable of generating an electrically usable signal for further processing directly from
the flow. The following equation basically applies:
U = k*B*D*v
where U = voltage, k = proportionality factor, B = magnetic field strength, D = tube
diameter, and v = flow velocity.
A possible realization of a magnetic inductive flow meter is disclosed in US 6,626,048
B1, whose entire disclosure is integrated herein by reference. Nevertheless, this
publication presents only the physical and electronic fundamentals but no practical
realization.
It is understood that major problems must be solved in the practical realization of a
magnetic inductive flow meter.

In one respect, this is a matter of the material. The measuring tube must be amagnetic
in order not to interfere with the magnetic field. The measuring tube further must be
electrically insulating in order not to interfere with the picking up of the voltage with use
of the electrodes. Moreover, the tube must consist of a food-safe material, when the
liquid is a food, for example, drinking water.
These requirements can be fulfilled best when a food-safe plastic is used as the
material. Nevertheless, plastics have the disadvantage of a much lower strength
compared with metal. Resistance to internal pressure, however, is an essential
requirement. The attempt to achieve internal pressure resistance with an increased
thickness of the tube wall is not practicable, because otherwise the magnetic field would
be weakened too greatly.
As mentioned above, the voltage at the measuring electrode is proportional to the
magnetic field strength, provided that the magnetic field permeates the measuring
channel homogeneously. US 6,626,048 B1 disclosed a solution for a circular cylindrical
measuring channel; this solution consisted of a magnetic coil with a magnetic core
made of ferromagnetic electrical sheet steel and two magnetic poles coupled to the
magnetic core and made of soft magnetic electrical sheet steel. Practical tests have
shown, however, that satisfactory measurement results cannot be achieved with this
arrangement. The reasons for this are the relatively long field lines and the high
magnetic resistance in the electrical sheet steel, because the magnetic circuit is
arranged around the electrodes.
Disclosure of the invention:
The present invention has as its object to provide a magnetic inductive flow meter,
which overcomes the aforementioned problems and provides an optimized
measurement result.
This object is attained by magnetic inductive flow meters with the features of claim 1.

A major advantage of the magnetic poles of the invention is the uniform distribution of
the magnetic field lines over the entire pole surface, produced by the double web on the
back of the magnetic poles. The distribution of the magnetic field lines can be influenced
by skillful dimensioning of the double web. At the same time, the punched, bent, and
folded part can be produced fully automatically and in large quantities.
According to an embodiment of the invention, the magnetic pole surfaces are triangular,
and the magnetic poles formed therefrom rectangular. Elliptical magnetic poles are an
alternative.
The double web produces additional advantages. If, according to an embodiment of the
invention, the magnetic core of the electromagnets or in any event at its ends is formed
flat, then it can be clamped between the double webs. The magnetic field lines
generated in the electromagnets are distributed optimally in this way and without an
attenuating air gap to both parts of the double web, which then transmits them further to
the surface elements of the magnetic pole.
To facilitate the assembly of the magnetic core of the electromagnets, the ends of the
double web can be splayed funnel-like.
To make possible the handling and positioning of the electromagnet, magnetic core,
and magnetic poles, according to a refinement of the invention, a plastic holder is
provided, which secures these parts in a clamping fashion.
According to a preferred embodiment, for this purpose, the plastic holder has an
approximate U shape with a stable cross web at the head end, two short legs, two long
legs parallel thereto, a groove between the long and short legs, matched to the
thickness of the double web and magnetic core, and lateral guides, which ensure the
correct position of the double web of the magnetic poles on the long leg.

This plastic holder has the advantage that the magnetic parts can be assembled using
simple plug-in procedures. The combination of the plastic holder and magnetic parts
can then be handled simply and securely and finally mounted in the magnetic inductive
flow meter.
According to a refinement, the long leg may end in a hook. This construction is of
advantage when the housing of the magnetic inductive flow meter is formed matching
thereto.
Brief description of the drawings:
The invention will be described in greater detail in the form of exemplary embodiments
with use of the drawing. It shows in:
FIG. 1 a punched/bent/folded part made of electrical sheet steel for the
production of a rectangular magnetic pole;
FIG. 2 a magnetic pole produced therefrom;
FIG. 3 as a front view an electromagnet with a flat magnetic core and two
magnetic poles according to FIG. 1, secured in a clamping manner in a
plastic holder;
FIG. 4 a side view to FIG. 3, and
FIG. 5 the plastic holder of FIG. 3 equipped with the magnetic parts, inserted in a
housing, cut crosswise, of a magnetic inductive flow meter.
Modes for carrying out the invention and industrial applicability:
FIG. 1 shows a punched/folded/bent part made of electrical sheet steel. Evident is a
long elongate strip 11', on which triangular surface elements 10.1, 10.2 are formed with

a mutual distance. A fold line 12 is provided on strip 11' between surface elements 10.1,
10.2. Bend lines 13 are provided between strip 11' and surface elements 10.1, 10.2.
FIG. 2 shows magnetic pole 10 resulting from the element of FIG. 1 by folding along line
12 and by bending along line 13. The two triangular surface elements 10.1, 10.2
complement each other to form a rectangular magnetic pole. The free ends of the
double web 11 are splayed funnel-like. Other shapes are readily possible for the
magnetic pole surfaces, e.g., rounded off, ovoid, etc.
A major advantage of this magnetic pole 10 apart from the simple production is the
optimal conduction of the magnetic field through double web 11 to the pole surfaces.
Furthermore, the flat ends of a magnetic core 27 of an electromagnet 26 (FIGS. 3 and
4) can be clamped between double web 11, so that the magnetic fields generated by
electromagnet 26 reach the pole surfaces optimally and without an interfering air gap.
FIG. 3 shows electromagnet 26 with a flat magnetic core 27, whose ends are clamped
between double webs 11 of two magnetic poles 10. Magnetic parts 10, 27 are in turn
secured in a clamping manner in a plastic holder 20. Plastic holder 20 has an
approximate U shape with a stable cross web 21 at the head end, two short legs 22, two
long legs 23 parallel thereto, a groove between the two legs 22, 23, matched to double
web 11 and magnetic core 27, and lateral guides 24, which ensure the correct position
of double web 11 on long leg 23.
The alternating magnetic field generated in magnetic coil 26 is transferred via magnetic
core 27 over a large area to double webs 11 and from these to magnetic poles 10, by
which the homogeneous magnetic field symbolized by double arrows is generated.
FIG. 4 shows the device of FIG. 3 as a side view. Magnetic core 27 can be seen
clamped between double web 11 and double web 11 clamped between legs 22, 23.
Further, at the lower end of long leg 23 a formed hook 25 can be seen, which

corresponds to a corresponding counterpart on the housing of a magnetic inductive flow
meter.
FIG. 5 shows plastic holder 20 of FIGS. 3 and 4 with the mounted magnetic parts 10,
26, 27, placed in a housing of a magnetic inductive flow meter, which is shown as a
cross section. The magnetic inductive flow meter has a rectangular measuring channel
31 with long side walls 32, against whose outer side magnetic poles 10 abut, in order to
generate the homogeneous magnetic field symbolized by double arrows in the interior
of measuring channel 31. Evident, further, is one of electrodes 34 which is placed in
measuring channel 31; these electrodes are oriented perpendicular to the magnetic field
and a measuring voltage can be picked up at them, which is proportional to the flow to
be measured.
FIG. 5, furthermore, shows in cross section an outer reinforcement cage for the
housing, consisting of two parallel, here perpendicularly oriented first longitudinal ribs 40
and two second longitudinal ribs 41 perpendicular thereto. Both longitudinal ribs 40, 41
end in a transverse partition 42, at whose back there is an inlet or outlet connecting
piece (not visible here) for the measuring fluid. Magnetic coil 26 is positioned next to
one of the two electrodes 34, namely, as close as possible. As a result, the magnetic
path from magnetic coil 26 via magnetic core 27 and double web 11 to the magnetic
pole surfaces becomes very short and electrode 34 remains freely accessible to pick up
the measuring voltage.
Finally, an inner transverse partition 37, which transfers the pressure exerted by the
internal pressure in measuring channel 31 on channel walls 32 to outer cage 40, 41, is
seen between walls 32 of measuring channel 31 and first longitudinal ribs 40.

We Claim:
1. A magnetic inductive flow meter with a pressure-resistant plastic housing, comprising
a measuring unit having
a measuring channel (31) having a rectangular cross section and through which
the measuring fluid flows,
a channel wall (32),
two opposing magnetic poles (10) at the channel wall (32),
an electromagnet with a magnetic coil (26) and magnetic core (27) for generating
an alternating magnetic field,
and two opposing measuring electrodes (34) in the channel wall (32),
characterized by the features:
the magnetic poles (10) are punched, bent, and folded parts made of electrical
sheet steel in the form of an elongate strip (11') with formed, mutually spaced-
apart surface elements (10.1, 10.2),
the elongate strip (11') forms a double web (11) after the folding,
the surface elements (10.1,10.2) form magnetic pole surfaces after the bending,
the double web (11) and the magnetic pole surfaces form the magnetic pole (10),
the double web (11) is located on the back of the magnetic pole (10).
2. The magnetic inductive flow meter according to claim 1, characterized by the
features:
the magnetic coil (26) is positioned next to one of the measuring electrodes (34),
the double web runs diagonal to the magnetic pole surfaces.
3. The magnetic inductive flow meter according to claim 1 or 2, characterized by the
features:
the surface elements (10.1,10.2) are triangular,
the magnetic pole surfaces form a rectangle,
the double web (11) is perpendicular to the magnetic pole surfaces.

4. The magnetic inductive flow meter according to claim 1 or 2, characterized by the
features:
the surface elements are rounded off,
the magnetic pole surfaces form an ellipse,
the double web (11) is perpendicular to the magnetic pole surfaces.
5. The magnetic inductive flow meter according to any one of claims 1 through 4,
characterized by the feature:
the magnetic core (27) of the electromagnet (26) is
-flat
- and clamped between the double webs (11).
6. The magnetic inductive flow meter according to any one of claims 1 through 5,
characterized by the feature:
the ends of the double web (11) are splayed funnel-like.
7. The magnetic inductive flow meter according to any one of claims 1 through 6,
characterized by the feature:
a plastic holder (20) secures the magnetic coil (26), the magnetic core (27), and
the magnetic poles (10) in a clamping fashion.
8. The magnetic inductive flow meter according to claim 7, characterized by the feature:
the plastic holder (20) has an approximate U shape with
- a stable cross web (21) at the head end,
- two short legs (22),
- two long legs (23) parallel thereto,
- and a groove between the two legs (22, 23), matched for a clamping fastening
of the double web (11) and magnetic core (27).
9. The magnetic inductive flow meter according to claim 7 or 8, characterized by the
feature:

lateral guides (24) ensure the correct position of the double web (11) on the long
leg (23).
10. The magnetic inductive flow meter according to claim 7, 8, or 9, characterized by the
feature:
the long legs (23) end in a hook (25).

ABSTRACT

The invention relates to a magnetically inductive
flowmeter having a pressure-resistant housing made of
plastic, comprising a measuring unit with a measuring
channel (31) of rectangular cross-section which is
flown through by the measurement fluid, a channel wall
(32), two opposing magnet poles (10) at the channel
wall (32), an electromagnet with magnet coil (26) and
magnet core (27) for generating a magnetic alternating
field as well as two opposing measurement electrodes
(34) in the channel wall (32) . The magnet poles are
punched, bent and folded parts made of electric sheet
metal in the form of an elongate strip (11') with
mutually distanced surface elements (10.1, 10.2) formed
thereon. The elongate strip (11') forms a double web
(11) after folding. The surface elements (10.1, 10.2)
form magnet pole surfaces after bending. The double web
(11) and the magnet pole surfaces form the magnet pole
(10) . The double web (11) is located on the rear side
of the magnet pole (10).